Diseases of the spine cause significant morbidity. These diseases include abnormalities of the vertebrae, the intervertebral discs, the facet joints, and connective tissue around the spine. These abnormalities can be due to a number of causes, including mechanical injury or degenerative disc disease. Such abnormalities can cause instability to the spine, allowing the vertebral column to become misaligned and producing micromotion between adjacent vertebrae. Vertebral misalignment and micromotion may result in wear to the vertebral bony surfaces and ultimately cause severe pain. Further, these conditions are often chronic and progressive problems.
The treatments for spinal disorders may include long-term medical management or surgery. Medical management is generally directed at controlling the symptoms, such as pain, rather than correcting the underlying problem. For some patients, this may require chronic use of pain medications, which may alter patient mental state or cause other negative side effects.
Another treatment option is surgery, which is often highly invasive and may significantly alter the spinal anatomy and function. For example, one surgical treatment for certain spinal conditions includes spinal fusion, whereby two or more vertebrae may be joined using bone grafts and/or synthetic implants. The fusion process is irreversible and may significantly alter vertebral range-of-motion. Further, current surgical procedures are often only applicable to patients in a significantly-progressed disease state.
Consequently, spinal surgeons have begun to develop more advanced surgical procedures and spinal stabilization and/or repair devices that are less invasive, may be reversible, and cause a less drastic alteration in the patient's normal anatomy and spinal function. These procedures may be used in an earlier stage of disease progression and, in some situations, may even stop or reverse disease progression.
Recently, a variety of interspinous stabilization devices have become available. These devices may be implanted between the spinous processes of two or more adjacent vertebrae. By stabilizing the spinous processes in this way, significant stress may be taken off the intervertebral discs to prevent disease progression or to improve conditions such as spinal stenosis. In addition, vertebral motion may be controlled without severely altering spinal anatomy.
Current interspinous vertebral implants are configured to be attached to the spinous processes of two or more adjacent vertebrae. Because the sacrum has a very small or non-existent spinous process, these devices cannot be implanted, for instance, between the fifth lumbar vertebra (L5) and the first sacral vertebra (S1). However, many patients have spinal conditions that affect the L5 and sacral vertebrae. It would therefore be desirable to provide improved interspinous vertebral stabilization devices, and in particular, devices that can be implanted between the sacrum and a lumbar vertebra.